JSON Validator: Check RFC 8259 JSON Syntax Online Free
JSON Validator checks pasted or dropped JSON against RFC 8259 and reports syntax errors with their exact line and column, plus a plain-language explanation of the likely cause. It also flags duplicate object keys and numbers that may lose precision. Use the results to locate problems and review the input before passing it to another parser or tool.
JSON Validator is a browser-based tool for checking whether JSON syntax complies with RFC 8259. Paste or drop your content to get a validation result, and use the reported line and column to find syntax errors. When an error is present, the tool also provides a plain-language explanation of its likely cause.
In addition to syntax errors, the validator warns about duplicate keys and numbers that may lose precision. These warnings help you review parts of the input that can be easy to overlook when reading JSON. The tool checks JSON validity; it does not describe schema validation or data conversion features.
JSON is a text-based format for representing structured data, including objects, arrays, strings, numbers, booleans, and null values. A JSON document can look reasonable while still containing invalid syntax, so validating it before another parser or tool consumes it can make troubleshooting more direct. The line and column report gives you a specific place to investigate rather than requiring a manual search through the whole input.
JSON Validator runs entirely in your browser. Your input is processed on your device and is not uploaded, stored, or sent to a server; after the page has loaded, the tool also works offline. It is free to use. Developers and DevOps engineers can use it to review JSON files, API content, or output from other tools at different stages of their workflow.
Step 1: Paste or drop your JSON into the tool. Add the complete content you want to check so the validator can inspect its syntax.
Step 2: Run the check to validate the input against RFC 8259. The tool reports whether it found a syntax error.
Step 3: Review any error details. Use the reported line and column, along with the plain-language explanation, to locate the likely cause.
Step 4: Check any additional warnings about duplicate keys or numbers that may lose precision. Make corrections in your source and run the check again.
Use case: Check a JSON file before it reaches a parser and fails at runtime. Finding syntax issues early helps prevent avoidable errors in a development workflow.
Use case: Locate a syntax error by line and column instead of searching through a large file by hand. The explanation can help you narrow down what to inspect.
Use case: Confirm that output from another tool is valid JSON, not just text that looks plausible. This is useful before passing generated content to another parser.
Use case: Review an API response or request body before using it in development. Validation can reveal malformed JSON before you investigate behavior elsewhere in your application.
Use case: Check a JSON configuration file after editing it. A quick syntax check helps catch mistakes before you use the file in a project.
Use case: Inspect JSON with repeated object keys or large numeric values. The duplicate-key and precision warnings can draw attention to details that may need review.